Waterproof paper and process of producing the same



Patented Sept. 3, 1929.

ALBERT L. CLAPP, OF DANVERS, MASSACHUSETTS, ASSIGNOR TO BENNETT, INCOR- PORATED, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

WATERPROOF PAPER AND PROCESS OF PRODUCING THE SAME.

No Drawing. Application filed February This invention has relation to the production of waterproof paper, using aqueous dispersions comprising a high proportion of dispersed particles of various unsaponifiable Y or diificultly saponifiable waterproofing materials, such as mineral oils, waxes, bitumens, gums, resins, asphalts, and like materials as sizing agents. The present invention has for one of its objects to provide a process of SlZ- ing pulp prior to its formation into paper, ,in an eflicacious and economical manner,

with such aqueous dispersions.

Dispersions of thermoplastic waterproofing material may be prepared by heating and meltin the material to be dispersed, and while in molten condition mixing it with vigorous stirring with a hot concentrated aqueous soap solution and continuing the stirring at a temperature above the melting I point of the material until the disperslon of particles are in molten condition and after they have become congealed, so that when K -the dispersion is subsequently diluted in water there is very little tendency for the particles to separate or float out.

Another procedure for forming a substantially stable or non-separating dispersion may be as follows. The thermo-plastic material is added, with stirring, to a hot aqueous solution of soap-formin constitufents, e. g., a fatty acid or fatty aci glyceride, and a solution of a suitable saponifying "agent, such as caustic soda, and the mass is stirred and maintained at a temperature 'above the meltin point of the thermoplastic material until tfie dispersion has been effected, whereupon the dispersion is allowed to cool. The cool dispersion comprises finely divided particles of congealed thermoplastic material, protected or filmed by the soap, formed from the reaction of the soap-forming constituents, which functions to prevent the formation of large agglomerates, during the dispersin procedure and after the dispersion has een effected, and produces a substantially stable, non-separating disper- $1011.

This dispersion is essentially similar to the 23, 1926. Serial No. 90,153.

dispersion produced by adding a molten thermoplastic material to a previously formed soap. When waterproofing materials fluid at atmospheric temperature, such as mineral oils, are employed, no heating would of course be necessary.

I have found that when a soap dispersion of waterproofing material such as described, containing a large proportion of unsaponified waterproofing material, is incorporated into pulp in the beater engine and precipitated with aluminum sulphate, alum, or other coagulating agents, a considerable proportion of the dispersed material remains behind as fine particles, and is not brought down and fixed on the stock together with the precipitated aluminum soap. In other words, the factor or retentivity of the dispersed material by the pulp is not optimum, a substantial percentage of such material be ing subsequently lost in the water removed during subsequent paper-forming operation, without performing a sizing or waterproofing function. For example, in employing a paraffin soap dispersion for sizing pulp which contains 1.5 to parts of paraffin to about parts of rosin size, it is found that it is uneconomical to incorporate more than 5% of parafiin into the pulp, because of the high loss of paraflin which results, due to separation of the paraffin after the coagulation of the dispersing agent. Moreover, it is uneconomical to operate with a dispersion containing a high percentage of paraffin or other like waterproofing material based on the weight of soap-dispersing agent, because of the consequent low retentivity resulting if high percentages of paraflin are employed, inasmuch as the soap serves the function of fixing the dispersed particles on the pulp.

In certain cases, however, it is desirable to incorporate higher than 5% parafiin or other waterproofing material into the stock so as to produce a paper'of high waterproofingquality, and to incorporate such waterproofing material without the introduction of an excessive quantity of aluminum resinate or other insoluble soaps, which are inferior as waterproofing or sizing agents to paraflin or other like unsaponified thermoplastic or waterproofing materials.

I have discovered that if the precipitation of an aqueous parafiin-soap dispersion or like dispersions of waterproofing material is effected in the presence of a soluble precipitable agent capable of uniting with aluminum sulphate or alum and forming a suflicient quantity of a voluminous or fiocculent precipitate, the dispersed, unsaponlfied particles of waterproofing material are brought down substantially in entirety, and together with the aluminum soap are fixed on the fibers of the pulp, thus resulting in a high factor of retentivity and hence a very low loss of such material in the water removed during subsequent paper-forming operation. Large percentages of paraffin or other waterproofing material may thus be economically employed for waterproofing paper.

The following example sets forth one method of procedure which may be employed in the preparation of a parafiin-soap dispersion which has been found to yield excellent results in sizing pulp. About 100 pounds of commercial rosin size (consist ing of 40 parts of dry rosin size and 60 parts of water) isheated to about 120 F. A heated mixture of silicate of soda and paraffin is formed by adding 40 parts of silicate of soda (60 Baum) to 40 parts of paraflin and, while stirring, heating the mixture above the melting point of the paraflin (say, 130 F.). To the heated solution of rosin size is added, with vigorous stirring, the heated mixture of silicate of soda and paraffin, and the mixed mass is stirred and maintained at a temperature of about 130 F. for about 15 to 20 minutes, whereupon the dispersion of the parafiin is completed. The dispersion is of a heavy, creamy consistency, and consists of fine, discrete particles of parafiin, enveloped by films of sodium resinate which serve to prevent the coalescence of the particles and to maintain the dispersion in substantially stable or non-separating form, so that upon dilution with water there is little tendency for the particles to separate or float out. The dispersion is preferably cooled prior to addition to the stock to be sized in the beater engine, so as to prevent a tendency to excessive foaming.

Another example of procedure for the preparation of a paraffin-soap dispersion may be about as follows. About 100 parts of commercial rosin size are added, with stirring, to about 40 pounds of paraflin, and are cooked together at a temperature of about 130 F. for about 30 minutes, whereupon the paraflin becomes dispersed as fine particles in the soap solution and yields a substantially stable, non-separating dispersion. About 40 parts of sodium silicate (60 Baum) is mixed into the dispersion and, preferably after allowing the mixture to cool, it may be incorporated into the stock to be sized in the beater engine. a

I prefer to employ the procedure described in the first example, because the dispersed particles appear to be in much finer condition and there is less tendency for the particles to agglomerate and separate out when diluted with water. This may be due to the fact that the dispersion is not only produced by the size (sodium resinate), but also by the sodium silicate, which itself is a very effective dispersing agent. Consequently, the combined dispersive effect is" greater than by the use of the rosin size or other soap alone.

The paraflin soap= dispersion thus produced may be added to the pulp in the beater engine prior to its manufacture into paper. About 180 pounds of dispersion may be added, for example, to size about 1000 pounds of sulphite pulp, which may be formed into paper of a highly water-resist ant and non-absorbent character, suitable for a great variety of uses. The addition of the dispersion preferably takes place during the last stages of after the completion of the beating operation, so as to avoid a tendency to excessive foaming. After the dispersion is incorporated into the pulp, the rosin and sodium silicate are simultaneously precipitated by the addition of aluminum sulphate or alum to the beater, about 150 to 200 pounds of alum being sulficient to ensure the precipitation of all the sodium silicate and rosin. The aluminum silicate comes down as a voluminous or flocculent precipitate, which, aided by the aluminum resinate soap, carries along therewith, or pulls down substantially all the finely dispersed particles of paraffin, and fixes them on the fibers of the pulp. The factor of retentivity of dispersed paraflin thus fixed on the stock is high and consequently large percentages of dispersed unsaponified material may economically be incorporated into pulp to produce paper having high waterproofing characteristics.

In the drying and calendering operations, the dispersed particles of paraffin are heated above their melting point, causing them to flux together with the aluminum resinate, and resulting in the melting and coalescence of the sizing particles throughout the paper. The preclpitated aluminum silicate serves as an admirable filler or loading material, and adds bulk and opaqueness to the paper.

he amount of sodium silicate added to the pulp should be regulated with the percentage of paraflin which is to be pulled down or precipitated on the pulp, and consequently if the percentage of paraflin is varied, the percentage of sodium silicate may also be correspondingly varied, but in any event, suflicient sodium silicate should be added to ensure a substantially complete retention of the paraflin' While I have described certain specific examples of procedure which have been found to yield desired results in papers suitable for certain uses, it is obvious that I factor appears to consist in the precipitation 55 may modify the percentages of the various agents as desired, depending upon the character of the paper which it is desired to pro- .duce and the uses to which it is to be put. The ercentage of paraflin in the disperslon, based on rosin or other soap, may be maintained as high as isconsistent with the production of a substantially stable or nonseparating depersion, but any other suitable proportion of paraflin to rosin may be used, if desired. I may also replace a portion or all of the 'paraflin by other waxes, such as Montan, carnauba, Japan, candelilla, or other unsaponifiable or difiiculty saponifiable waterproofing material, and a portion or all of the rosin, by other soaps, such as sodium oleate, sodium palmitate, sodium stearate, and the-like.

It is also ossible to change or modify the procedure om that described in" these specific examples. Thus I may incorporate the soap-parafiin dispersion into the stock in the beater engine, and add sodium silicate separately thereto; or I may first add the aluminum sulphate or alum to the stock and subsequently. incorporate the paraffin-soap dispersion and sodium silicate, but the procedure set forth in the examples given has generally been found to be more expedient. Other sizing and filling agents may also be used together with those agents mentioned. The dispersion may also be successfully employed in the sizing of various pulp furnishes.

a In canying on experimentation connected with the 'scoveries disclosed herein, I found that I may substitute caustic soda or caustic lime, or equivalent alkaline compounds, for the sodium silicate, and produce a precipitate of aluminum hydrate which also performs the function of carryin down therewith the dispersed particles 0% unsa onified waterproofing material. The re ts producedthereby, however, are inferior to those obtained by the use of sodium silicate, and the retentivity of dispersed particles by the stock is lower, also a larger quantity of alum must be used.

This is doubtless due to the fact that the aluminum'hydrate is of much lower bulk than the aluminum silicate precipitate, and

consequently does not carry the dispersed particles down as efliciently. The essential of a voluminous or flocculent precipitate, which carries down therewith the fine particles of unsaponified dispersed thermoplastic material and fixes them on-the fibers of the pulp together with the insoluble soap formed from the soluble soap which serves as the dispersing agent.

I claim:

1. A process of sizing paper, which comprises incorporating into pulp prior to its formation into paper, an aqueous soap dis persion of unsaponified waterproofing material, together with a substantial quantity of sodium silicate, and adding suflicient aluminum sulphate to precipitate the soap and sodium silicate, thereb forming 9. voluminous precipitate of a uminum silicate carrying down and fixing substantially all the dispersed material on the pulp.

' 2. A process of sizing paper, which comprises adding to pulp prior to its formation into paper, an aqueous soap-sodium-silicate dispersion of unsaponified. waterproofing material, and adding suificient aluminum sulphate to precipitate the soap and silicate thereby forming a voluminous precipitate of the aluminum silicate carrying down and fixing substantially all the dispersed material on the pulp.

t} A process of waterproofing paper, which comprises incorporating into pulp prior to its formation into paper, an aqueous sodium resinate dispersion of unsaponified waterproofing material, together with a substantial' quantity of sodium silicate, and adding sufiicient aluminum sulphate to precipitate the sodium silicate, thereby forming a voluminous precipitate of aluminum silicate carrying down and fixing substantially all 'the dispersed material on the pulp.

4. A process which comprises incorporating into paper pulp an aqueous sodium resinate dispersion of thermoplastic waterproofing material together with sodium sili cate, adding alum in suflicient quantity to precipitate substantially all theresinate and silicate, running the pulp out on a paper machine, and fusing the thermoplastic material in the paper. V

In testimony whereof I have aflixed my signature.

ALBERT L. CLAPP. 

